There is an increasing desire for a power supply that can independently control two or more high-powered loads using an AC wall outlet while introducing a reduced amount of harmonics and/or flicker into the power grid. The urban population is increasing, and with it there is an increasing desire for high powered loads that can be plugged into an AC wall outlet. By way of example, urban dwellers live in apartment or condominium buildings where they would like to use a grill. Because of smoke, gas, or other concerns, use of typical charcoal or gas grills may not be permitted or desirable.
There are a number of available electric cooking devices, such as the George Foreman Plate Grill (and similar devices), Panini presses, electric griddles and the like. However, these prior art devices generally do not deliver variable power. Moreover, these prior art electric cooking devices typically cannot generate enough power to match a gas or electric grill.
Some prior art devices may use variable resistors in series with electric loads to control an amount of power delivered to the load. For example, as the resistance of a variable resistor increases, the variable resistor restricts power from being delivered to an electric load. The use of variable resistors to control power delivery to electric loads is well known. But variable resistors come with disadvantages. For example, disadvantages may include the introduction of harmonics onto the electrical system, which translates to electromagnetic emissions that can create interference and other unpredictable electromagnetic fields. Moreover, variable resistors may be inefficient because they burn a lot of power.
Other prior art devices may use a bi-metal thermometer which opens and closes to control power delivery. Disadvantages of using a bi-metal thermometer include the fact that it allows for less discrete (i.e., less precise) control over power delivered and is usually associated with a relatively long lag in response time. A long lag time causes a negative cooking experience because it leads to poor control over temperature. Moreover, a long lag time is disadvantageous because long on/off duty cycles are known to shorten the life span of a heating element
Some devices may use half-wave control techniques to deliver power. For example, U.S. Pat. No. 6,772,475, titled “Heating Control System Which Minimizes AC Power Line Voltage Fluctuations,” discloses half wave AC control devices to control delivery of AC current. This control method is associated with significant disadvantages because it delivers power only in stages, not in a continuous range from 0-100%. By contrast, embodiments of the present invention allow continuous variable power delivery.
Yet other prior art devices may include a digital control for limiting the in-rush of electric current when an electric load in turned on. For example, U.S. Pat. No. 6,111,230, titled “Method and apparatus for supplying AC power while meeting the European flicker and harmonic requirements,” describes a method for limiting the in-rush of current to a printing device when it is first turned on. However, the disclosed devices do not provide for independently controlling multiple electric loads, much less for reducing harmonic currents and flicker while independently controlling multiple loads.
Thus, there is a need for a digital power supply that can independently control two or more electric loads while introducing only reduced harmonic and flicker interference to the power system.